Devices for enriching drinking water with carbon dioxide (also designated by carbonation of drinking water) have been known for a long time. In most of these devices, carbonation of the drinking water occurs in a storage container. Recently, however, devices have also been developed for enriching tap water in the home or restaurants with carbon dioxide in a continuous process. In the continuous process without any storage container, carbonation takes place in a flow-through mixer which is directly connected to the drinking water pipe. As compared with standard devices with a storage container, carbonation of tap water in the continuous process without any storage container has the advantage of being essentially more compact, economical and further also hygienic. In direct comparison with carbonation devices with a storage container, the quality of the carbonation of tap water in the continuous process without any storage container however still leaves a great deal to be desired. A problem is also i.a. that the pressure in the drinking water pipe may be between 2 bars and 6 bars, and that the flow-through mixer has to be adapted consequently to very different water pressures.
A device for enriching drinking water with carbon dioxide in the continuous process is for example described in WO 2004/024306. The flow-through mixer has a nozzle annular gap for water and a central gas injection. The pressure in the flow-through mixer is maintained constant by means of an overflow valve in the tapping pipe and an additional pressure stabilizer in the flow-through mixer itself. Further, a flow rate valve is positioned in the gas feed pipe, which should maintain constant the amount of gas fed into the flow-through mixer per unit of time. Further, the control comprises a solenoid valve in the water connection, and a solenoid valve in the gas connection of the flow-through mixer. Both solenoid valves are closed, in the case when a pressure monitor in the tapping type detects a pressure increase above the working pressure. Here, this is a relatively costly control technique, the fine adjustment of which is also relatively complicated. Further, the flow-through mixer only operates relatively perfectly for pressures above 3.5 bars.
An industrial device for enriching drinks with carbon dioxide is for example described in U.S. Pat. No. 5,842,600. In this industrial device, the gas is fed into a Venturi nozzle in a water stream. In this Venturi nozzle, the water flows out of a central nozzle, which is surrounded by an annular gap, from which the gas flows into the Venturi nozzle. Subsequently, water and gas are mixed in a static mixer tube. The water pressure is maintained constant by means of a pressure controller and a pump, so that carbonation always takes place under optimum conditions.
In EP 0322925, a Venturi arrangement is described for dispersing gas in a liquid stream. In a Venturi nozzle, the gas is fed with a type of injection needle before constriction axially in the Venturi nozzle. In order to optimize the result of the gas dispersion, the flow velocity of the gas bubbles/liquid mixture in the convergent section of the Venturi nozzle increases to a velocity lying above sound velocity, so that subsequently in the divergent section of the Venturi nozzle, it is again lowered to a velocity lying below the sound velocity. This of course means that a predetermined admission pressure of the liquid stream must be strictly observed.
A Venturi nozzle for carbonation of drinking water is known from EP 1579906. The latter has an inlet section converging in the direction of flow and an outlet section diverging in the direction of flow, which are connected through a constriction which is formed as a cylindrical channel. A gas channel opens into the constriction of the Venturi nozzle, the longitudinal axis of the gas channel being perpendicular to the longitudinal axis of the cylindrical constriction. Four longitudinal ribs are positioned in the divergent outlet section of the Venturi nozzle, which should prevent degassing of the water.